Draft: Editor Lite live preview for Markdown files

What does this MR do?

Introduces the new menu action for toggling live-preview for markdown files. The same functionality can be toggled by ⌘+K V keystroke combination that matches that of VSCode.

Screenshots (strongly suggested)

EditorLite-markdown-preview

⚠ The typo in the word "title" is something that sneaks into majority of my demos 🤦

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

References #280798 (closed)